Experimental and numerical investigation of T section connections

The paper summarizes recent experimental research on determining the full-range behaviour of steel beam-to-column connections. Unlike the connection types in the literature, numerical modeling was done with various experiments to determine the behavior of two types of connection types. In these joints, T joints have been studied, but unlike the literature, T joint's element is made of plates; It was obtained from 1/2 IPE profile, not by welding. Thus, it is thought that the problems such as workmanship errors, break point formation and in situ welding failures, which occur in the welding of T joints, are eliminated. Necessary studies have been carried out to have sufficient information about the behavior of the T joint to be manufactured from the IPE profile and thus to provide the opportunity for its use. In the light of the data obtained, numerical modeling is done and the torque rotation relation and behavior of semi-rigid joints are numerically modeled. Thus, thanks to the calibrated model with the experiments, the closest results to the real behavior were obtained for the unexamined combinations.

Analysis of Changes in Parameters of Free Vibration of Single and Multi-span Girders with Semi-rigid Joints

This study presents the analysis carried out for changes in parameters of free vibrations of single-span corrugated web girders with a semi-rigid joint at midspan and multi-span girders with spans connected by semi-rigid joints. Based on the experimental tests and the theoretical analysis, the behavior of six simply supported girders with the semi-rigid joint at midspan was analyzed. They were straight and double-slope girders with a span of 6.02 m, made of corrugated web sections WTA 500/300x15 with different types of semi-rigid end plate joints. It was demonstrated that the variable rotational stiffness Sj of the joint affected the equivalent concentrated mass of the girder mz, the frequency of damped free vibrations α, damping ρ, and the frequency of free vibrations ω. The theoretical analysis was conducted for a change in the equivalent concentrated mass of the single-span girders fixed at both ends and of the multi-span girders. It was described how the change in the support stiffness in the single-span girders fixed at both ends and the change in joint stiffness of spans affected the equivalent concentrated mass mz as a function of non-dimensional stiffness k. The equivalent concentrated mass mz of the girder was found to affect the values of maximum vibrations in the structure. A continuous change in the rotational stiffness of joints was taken into account from the pinned to the rigid joint.

Research of changes in the parameters that affect the rigidness of the column-foundation joints

Introduction. The existing types of connection assignment in the design scheme — hinged and absolutely rigid joints — do not reflect the actual operation of the connection. The lack of calculation of the actual rigidness of joint and its failure to take into account in the design of the frame can lead to a different distribution of efforts from the calculated one and an increase in the movement of the frame elements. The purpose of this work is to researching the influence of the change size of the elements forming the column base on its rotational rigidity. Materials and methods. The calculation of the transverse frame was performed in the Dlubal RFEM software package. The calculated efforts acting in the lower section of the column were transferred to the calculated models of the column base, made in the IDEA StatiCa software package, in which the further calculation of the joint rigidness was performed. Results. The rotational rigidness of the joints with different structural solutions of the column base is determined. The change in the rigidness of the connection between the column and the foundation with an increase in the thickness and height of the support ribs is analyzed. Based on the calculations, graphs of the identified dependencies are constructed. As an example of strengthening the base of the column, the introduction of a traverse was proposed. The article considers six variants of the traverse device, and variants with three support ribs and with traverses, but without support ribs. The calculated rigidness of the column bases is summarized in graphs, where it can be seen that the metal adding is effective only up to a certain point. Variants of the arrangement of column bases with additional transverse ribs are considered. Conclusions. The greatest contribution to the increase in the rotational rigidness of the joint is made by the addition of a traverse. By increasing the thickness or height of the introduced traverse, it is impossible to achieve absolutely rigid fixing, it is necessary to change several parameters in a complex way. The introduction of additional ribs located outside the plane of action of the moment practically does not affect the rigidity of the joint.

Seismic Fragility Curves for Performance of Semi-rigid Connections of Steel Frames

A steel frame with a semi-rigid connection is one of the most widely used structural systems in modern construction. These systems are cheap to make, require less time to construct and offer the highest quality and reliable construction quality without the need for highly skilled workers. However, these systems show greater natural periods compared to their perfectly rigid frame counterparts. This causes the building to attract low loads during earthquakes. In this research study, the seismic performance of steel frames with semi-rigid joints is evaluated. Three connections with capacities of 50, 70 and 100% of the beam’s plastic moment are studied and examined. The seismic performance of these frames is determined by a non-linear static pushover analysis and an incremental dynamic analysis leading finally to the fragility curves which are developed. The results show that a decrease in the connection capacity increases the probability of reaching or exceeding a particular damage limit state in the frames is found. Doi: 10.28991/cej-2021-03091714 Full Text: PDF

Design, Modeling, and Control of an Autonomous Legged-Wheeled Hybrid Robotic Vehicle with Non-Rigid Joints

This paper presents a legged-wheeled hybrid robotic vehicle that uses a combination of rigid and non-rigid joints, allowing it to be more impact-tolerant. The robot has four legs, each one with three degrees of freedom. Each leg has two non-rigid rotational joints with completely passive components for damping and accumulation of kinetic energy, one rigid rotational joint, and a driving wheel. Each leg uses three independent DC motors—one for each joint, as well as a fourth one for driving the wheel. The four legs have the same position configuration, except for the upper hip joint. The vehicle was designed to be modular, low-cost, and its parts to be interchangeable. Beyond this, the vehicle has multiple operation modes, including a low-power mode. Across this article, the design, modeling, and control stages are presented, as well as the communication strategy. A prototype platform was built to serve as a test bed, which is described throughout the article. The mechanical design and applied hardware for each leg have been improved, and these changes are described. The mechanical and hardware structure of the complete robot is also presented, as well as the software and communication approaches. Moreover, a realistic simulation is introduced, along with the obtained results.

A CAD model for the tolerancing of mechanical assemblies considering non-rigid joints between parts with defects

During the design stage, the ideal simulation and visualization of the mechanical assemblies behavior require the modeling of parts with dimensional and geometrical defects. However, the deviations caused by parts deformations can generate an important difference between the ideal assembly and the real product. In this regard, this paper proposes a tolerance analysis method of CAD assemblies considering non-rigid joints between parts with defects. The determination of realistic rigid components with dimensional and geometrical defects is based on the worst case tolerancing approach and the Small Displacement Torsor (SDT) parameters. The Finite Element (FE) computation is executed to determine deformations of realistic non-rigid part models under external loads. Sub-algorithms to define non-rigid joints between realistic parts are developed. The tolerance analysis is established using the realistic CAD assembly. A case study is presented to evaluate the proposed model.

Joint Equivalence Design and Analysis of a Tensegrity Joint

We propose a method to design a tensegrity joint, making its elastic deformation an accurate joint-like motion, such as a rotation around the designed rotational center. The tensegrity joint can be a three rotational degree-of-freedom (DOF) joint through this method. Axis drift is presented as a design criterion to describe the rotational center's deviation degree concerning the compliance center since the rotational center is not fixed to one point for different positions of the tensegrity joint. The axis drift is designed to be in a prescribed range so that the tensegrity joint is approximately equivalent to a rigid joint. In other words, the tensegrity joint's elastic response under external torque and force becomes precise rigid-joint-like kinematics and can replace rigid joints to transfer motion, force, and energy. A large-size tensegrity joint is developed to verify the joint equivalence experimentally. The experimental results show that the tensegrity joint achieved maximum dimensionless axis drift less than 2%, and indicate an excellent joint equivalence. The tensegrity joints' ability to replace rigid joints as modular joints to construct a hyper redundant serial structure is demonstrated using a tensegrity robotic arm. The proposed tensegrity compliant joint has notable benefits of tensegrity structure such as high mechanical efficiency, modularity, and scalability, and can be extended to many robotic applications, such as large-size serial robotic arms and snake-like robots.